Suppression of T-bet+ B cells in lupus by tryptophan metabolites

About This Grant

PROJECT SUMMARY This proposal aims to (i) identify immunoregulatory metabolic signals induced by IL-4 that suppress TLR7 stimulation of lupus pathogenic B cells including T-bet+ B cells, and (ii) develop safer SLE therapeutics using immune-regulatory metabolites to inhibit TLR7-induced lupus pathogenic B cell development. Our recent findings show that in SLE, reduced IL-4R expression and defective maintenance of naïve B cells contribute to increased T-bet+CD11c+ B cells and autoantibody development. Co-culture with IL-4 blocked interferon- promoted development of T-bet+CD11c+ B cells and preserved a T-bet−CD11c− phenotype. IL-4 treatment in vivo suppressed a TLR7 ligand R848-promoted development of T-bet+ age-related B cells (ABCs), germinal center (GC) dark zone B cells, CD138+ plasma B cells (PBs), and autoantibody in BXD2 mice. Preliminary data from lupus BXD2 mouse B cells treated with IL-4 revealed upregulation of IL4i1, which generates indole- 3-pyruvic acid (IPyA) from tryptophan (Trp), and metabolites including kynurenine (Kyn) that activate the aryl hydrocarbon receptor (AhR) pathway. In the absence of IL-4, AhR agonists including Kyn and 6- Formylindolo[3,2-b]carbazole (FICZ) suppressed T-bet+CD11c+ B cell development and preserved naïve B cells. A deficiency of AhR in B cells enhanced TLR7 ligand-induced T-bet+ B cell development in vivo and nullified FICZ suppression of T-bet+ B cells in vitro. We hypothesize that IL-4 stimulates IL4i1-mediated IPyA and Kyn to inhibit ABC, GC, and PB development via AhR activation. Aim 1 will determine the Trp metabolic signals induced by IL-4 to inhibit TLR7-induced lupus autoantibody precursor B cells including ABCs and GC B cells in vivo. The induction and essential role of B-cell endogenous IL4i1, Ido1, and AhR for IL-4 suppression of lupus pathogenic B cell development will be determined in wild-type (Aim 1A) and knock-out mice (Aim 1B). Aim 2 will determine what IL-4-induced Trp metabolites can effectively suppress TLR7-mediated ABCs and GC B cell development in vivo. The primary metabolites that activate the AhR program and can be induced by IL-4 in vivo in B cells will be determined (Aim 2A). Whether these metabolites can suppress TLR7-induced development of ABCs, GC B cells, and autoantibodies will be determined (Aim 2B). Significance: This research shifts focus from pro-inflammatory factors to strategies that restore immune cell homeostasis, potentially offering safer SLE treatments. Innovation: The proposed project aims to discover metabolites that regulate B-cell homeostasis, offering novel, druggable targets for SLE therapy. Team and Environment: Dr. Mountz specializes in cytokine-mediated B-cell transcriptomics in SLE, while Dr. Barnes, Director of UAB's TMPL, will provide metabolomics expertise. Dr. Corinne Augelli-Szafran who specializes in small molecule drug discovery will be a collaborator to assist in developing the hit-to-candidate pipeline of Trp metabolite prioritization and screening.